In general, dielectric ceramic materials of a lead titanate system have widely been used as a dielectric material for ceramic capacitors because of its relatively high dielectric constant and a low sintering temperature. For example, lead titanate dielectric ceramic compositions have been applied to monolithic or multilayer ceramic capacitors. Such multilayer ceramic capacitors are generally fabricated by first preparing ceramic green sheets, printing a conductive ink for internal electrodes (composed of metal powder suspended in an organic vehicle) in the designed pattern on the ceramic green sheets, bonding several printed green sheets one on another under heat and pressure, cutting the resultant stack into individual capacitor units, and firing them to complete multilayer ceramic capacitor units.
Most of the conventional dielectric ceramic materials for multilayer ceramic capacitors must be fired in an oxidizing atmosphere since these ceramic materials are reduced to a semiconductive material when fired in a reducing atmosphere with a low partial pressure of oxygen. For this reason, it is required to use a noble metal such as, for example, Ag--Pd alloys, which are stable even in an oxidizing atmosphere at a high temperature, as a material for internal electrodes.
However, the noble metal materials are expensive and causes lowering of dielectric properties since migration of Ag takes place during sintering. Also, the Ag--Pd alloys are low in electric conductivity.